This invention relates to a fluid power actuator and particularly to such an actuator having an integrated mounting means.
Fluid actuators of the piston type are employed to provide reliable, low cost controls particularly where substantial loads and a compact construction are required. Pneumatic operators are widely employed because of the simplification permitted by the use of air and the readily available air sources in commercial, industrial and like applications. In particular, in environmental control systems and the like, pneumatic actuators are employed for positioning of various controls. A heating, ventilating and air conditioning system for example normally includes dampers for proper directing of the air throughout the system. In such systems, the room air may be recirculated through the system and selectively mixed with selected amounts of fresh air in a suitable mixer box. Dampers are employed to control the relative proportions of the recirculated air and fresh air. Within the system, the treated air is routed through different ducts to the various areas, with the amount and direction also controlled by suitable dampers. Pneumatic damper actuators are conveniently employed to establish a proportional and/or on-off setting of the dampers in response to various sensed conditions. In any given institutional or commercial installation, a substantial number of individually controlled dampers might be employed to provide optimum air flow.
A satisfactory actuator found in the prior art employes a piston-cylinder and diaphragm construction. Generally, a diaphragm has its periphery secured to the wall of a cylinder unit and secured to the face of a piston. The diaphragm defines a signal chamber connected to a suitable air pressure signal source to receive a suitable pressure signal from a controller. The piston-diaphragm are spring-loaded to an initial position with a minimum input signal and provide a working stroke over a selected pressure signal range. The actuator will generally be provided with a mounting bracket for mounting of the actuator to the damper assembly with the piston rod interconnected to the damper control or to the damper element through a suitable linkage. Generally, in a variable volume damper of a high velocity mixing box for an air conditioning system, a system pressure range of 15 to 25 PSI may be available but is more typically 15 to 20 PSI. The actuator spring-loading is typically designed to cover spring ranges of 5-10, 8-13, and 10-15 pounds per square inch (PSI).
For purposes of economy and practical implementation, the prior art has developed low cost, expendable or throw-away actuators for convenient original installation and maintenance of relatively large system. Generally, such prior art devices have employed a molded plastic construction of the cylinder unit and piston. The cylinder is generally a cup-shaped member with a separate head secured to the open end. A piston is located in the cylinder unit with a piston shaft projecting through the one end of the cylinder and with a spring biasing the piston to retract the piston rod. A diaphragm is secured to the face of the piston with the periphery of the diaphragm clamped between the cylinder head and the cylinder to define the signal input chamber to the side of the diaphragm opposite the piston. The control signal applied to the input chamber forces the piston and piston rod to move and compress the spring in accordance with pressure level. The construction is preferably such as to provide a linear output movement, with the pressure signal for corresponding positioning of the dampers or other load.
The several components of the throw-away type plastic actuators should be uniquely adapted to mass production while permitting a construction having a high degree of reliability and reasonable life. Actuator manufacturers often supply various original equipment manufacturers of different systems to obtain the maximum benefits of mass production. The actuator must, however, be compatible with the widely varying specification as to size, mounting and interconnection to the particular load.
Although such unit is available, it generally is provided with special mounting members for adaptation to various mounting specifications. The working stroke may also be different in different loads and applications. Generally, a preset stroke with an adjustable linkage or suitable adjustment screw stops may be provided to adapt the actuator to different stroke requirements.
In summary, although satisfactory relatively inexpensive plastic actuators have been designed, there is a need for a highly versatile reliable actuator which can be directly adapted in a convenient and inexpensive manner to the widely varying specifications encountered in the field and in the industrial arts, particularly in the heating, ventilating and air conditioning damper control applications.